The present invention relates generally to a reference circuit for the generation of a reference voltage and, in particular, to a band-gap reference circuit that generates voltages and currents independent of process, voltage, and temperature.
Band-gap reference circuits are used to generate precise voltages and currents. The generated voltages and currents are independent of process, voltage, and temperature. Band-gap reference circuits are used in various analogue and digital circuits that require precise voltages or currents for operation. In particular, the generated voltage is used as a bias voltage in circuits such as Analogue to Digital (A/D) converters and constant current generators. In conventional band-gap reference circuits, a reference voltage is generated across a resistor by passing a suitable current through the resistor.
Current generators are used for generating a current that enables generation of the required reference voltage across the resistor. Current generators usually include a Proportional to Absolute Temperature (PTAT) current generator, and an Inversely Proportional to Absolute Temperature (IPTAT) current generator. The PTAT current generator generates a current that is proportional to the absolute temperature, whereas the IPTAT current generator generates a current that is inversely proportional to the absolute temperature. The currents generated by these two current generators are added to generate a current that is independent of the absolute temperature. This generated current is then passed through a resistor and the required reference voltage is generated across the resistor.
In conventional band-gap reference circuits that use the Complementary Metal Oxide Semiconductor (CMOS) technology, good quality resistors are required for current generation. Such resistors require extra mask sets, which adds to the fabrication costs of the circuit. Further, conventional band-gap reference circuits are not suitable for generation of very low reference voltage levels, such as 1 Volt and lower. Hence, the conventional circuits cannot be used in circuits made with low voltage process technologies, such as CMOS90.
Accordingly, there is a need for a band-gap reference circuit that is suitable for generation of low operational voltage levels, and that may be readily fabricated at reasonable cost.